Die-cast masonry drill with leading hard insert

ABSTRACT

A masonry drill and method for its manufacture are disclosed. The drill has an axially elongated body which is made from a die cast material and has one or more spiral grooves cast in its exterior surface substantially along its length. A hard insert is embedded in the leading end of the body. The insert is formed with sides having generally planar side portions, a top chisel edge, and a bottom edge. The insert preferably has means for interlocking with the body, the interlocking means preferably comprising a projection extending from the plane of each of the side portions. Each projection extends the greatest distance from the plane of the side portions near the bottom edge of the insert. The insert is held in place by casting the body around it so that the body substantially surrounds the projection, and especially entirely covers the portion of the projection nearest the chisel edge. As the die cast material of the body cools following the casting operation, it contracts around the insert to securely hold the insert in place. An extremely economical yet rugged drill is thus formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the construction of drills, and particularlyto drills which are specially adapted for drilling masonry, stone, rock,concrete, cement, cinder block, and the like.

2. Description of the Prior Art

Masonry drills have been known and are commonly used for drilling holesin especially hard friable material such as masonry or stone. Thesedrills are usually comprised of an elongated body or shank having aspiral groove or grooves formed along their length and having adiametrically extending straight groove on their leading end. A hardinsert was provided in the straight groove and was held in place bysoldering or brazing. The insert usually had sharp cutting edges on itsleading end so that the drill might effectively be used in the hardmasonry or stone material. The spiral groove provided a channel for thedischarge of chips, particles, dust and other drilling debris loosenedby the leading end of the drill during the drilling operation. Theinsert must be capable of resisting wear, fracture, and the abrasiveaction of the chips from the material being drilled, while the body ofthe drill must maintain sufficient strength in the presence of heatgenerated in use.

In the manufacture of prior art masonry drills, it has been the practiceto make the drill body of a material such as steel and to mount theabrasion-resistant insert or cutting elements at the cutting end. Thebody of the drill was normally formed by conventional rolling, machiningor grinding the spiral thread in a blank or rod of suitable length. Thestraight groove for the mounting of the insert or cutting element wasthen machined in the leading end of the drill body, and the cuttingelement was placed and secured. The cutting element was formed of a hardmaterial such as tungsten carbide and was usually anchored in place inthe body of the drill by soldering or brazing it in place.

Examples of prior art masonry drills are shown in the following U.S.Pat. Nos.: 2,879,036 issued to Wheeler; 2,902,260 issued to Tilden;3,372,763 issued to Fischer; 3,447,616 issued to Granat; 3,469,643issued to Horst; 3,674,101 issued to Chromy; and 3,845,829 issued toSchaumann.

The manufacture of prior art masonry drills by these known processes hasbeen relatively expensive. The initial expense of these masonry drillsmay be offset somewhat in industrial use by resharpening the hardenedinsert or cutting element a number of times. While satisfactory butexpensive industrial quality masonry drills have been manufactured bythis process, it has not been possible to provide inexpensive yet highquality masonry drills for nonindustrial users. The initial expense of amasonry drill provided to consumers through retail outlets such ashardware stores may not be offset by resharpening, since the averagenonindustrial user generally does not have the capability ofresharpening carbide tips. In addition, the tools purchased bynonindustrial users are often purchased for very limited use, such as todrill several holes needed for a particular job, and the drill may notbe used again thereafter since the user may not have occasion to do so.

An additional cost associated with the manufacture of masonry drills ofthe prior art was the cost of inserting and soldering or brazing thecutting element or insert in place. Since it is important that theinsert be firmly anchored in the drill body, there did not appear to beany means for eliminating this step in the manufacturing process.

There is presently a need for an inexpensive tool that will performsubstantially equivalent to the conventional masonry drill yet will costsignificantly less. The usable life of the body of such a drill needonly be as long as that of the carbide tip, since the tip would probablynot be resharpened. However, it is possible that such a drill may beresharpened, so that it would be advantageous if the body would outlastthe tip.

It may be possible to reduce the cost of manufacturing with conventionalmethods, but this may require a major expenditure and an assurance ofhigh volume production. Even with conventional methods, moreover, thecost reductions would not be significant.

SUMMARY OF THE INVENTION

The present invention overcomes many of the difficulties andshortcomings of the prior art masonry drills and affords other featuresand advantages heretofore not obtainable. The present invention providesa masonry drill which includes a hard drilling tip formed of an insertand which may be manufactured more economically than drills of the priorart. In accordance with the present invention, the body of the drill isformed by a die casting process, whereby the spiral groove or grooves inthe body of the drill may be formed economically in a single processwithout expensive machining, rolling, or grinding. In addition, the hardcutting insert is cast in place on the leading end of the drill body,thereby eliminating the additional processes of forming a groove on theleading end of the drill body, placing the cutting insert into thegroove, and soldering or brazing the insert in place.

In accordance with another aspect of this invention, the hard cuttinginsert is provided with interlocking means for securing the insert tothe drill body. In the preferred embodiment of the invention, theinterlocking means comprises a pair of projections on the insert each ofwhich extends from one side of the insert with the cast drill bodysubstantially surrounding the projections and securely holding theinsert in place. The insert is also secured by the metal from the bodyof the drill as it cools following the casting operation and contractswith respect to the insert as a result of the differences in rates ofthermal expansion between the insert and the casting material used informing the body of the drill.

The particular design of the interlocking means is important to theinvention, since the coefficient of thermal expansion of the metal usedin the formation of the cast body of the drill is significantly greaterthan the coefficient of thermal expansion of the material used in thetip, such as tungsten carbide. Therefore, in forming an interlockbetween the tip and the body, it is possible that the material of thedrill body may contract away from a portion of the surface of the insertat certain places as the body cools following the casting operation. Ifthe drill body contracts away from the surface of the insert, it maycreate gaps which would weaken the drill and the connection formedbetween the insert and the body.

In accordance with another aspect of this invention, the interlockingmeans is designed to avoid additional steps in the manufacturing processof the insert. The interlocking means preferably comprises a pair ofprojections which extend on each side of the insert from the plane ofthe flat side portions of the insert with each projection taperinginwardly to the plane of one of the flat side portions as the projectionextends toward the cutting end of the insert and with the cast materialof the body substantially covering the portion of the projectionextending toward the cutting end of the insert, so that the drill insertcannot be removed axially from the drill, providing a more secureconnection between the insert and the body by utilizing the contractionof the drill body around the insert.

The interlocking means of the present invention is designed to avoidloss of strength in the insert by avoiding any reduction of thethickness of the insert which may result from using cutouts or providingholes in the insert as part of an interlocking means. Such holes orcutouts may result in weakening of the insert and in drill failure. Inaddition, the insert is also secured in the body of the drill at theleading or cutting end of the drill by utilizing the thermal contractionof the cast material of the body of the drill as means for holding theinsert in place, so that the invention does not rely solely upon themechanical interlock provided by the projection as the means forsecuring the insert in place.

These and other advantages are accomplished by the die cast masonrydrill of the present invention, which comprises an axially elongated,generally cylindrical body having a leading front end portion and rearend portion. The rear end portion is adapted to be held by a toolholder. The body is formed of a die cast material, preferably a zincalloy, and has a spiral groove or grooves cast in its exterior surfacesubstantially along its length. A hard insert is embedded in the leadingend of the body. The insert is generally flat and extends generallydiametrically across the leading end of the body. The insert has on eachside parallel flat side portions and a chisel edge extending across thetop between the sides with leading cutting edges on either side of thechisel edge. The insert also has a bottom edge opposite the cuttingedges. The insert has means for interlocking with the body. Theinterlocking means comprises one or more projections or pairs ofprojections, one projection on each side extending from the plane of theflat side portion. Each of the projections extends the greatest distancefrom the plane of the side portion near the bottom edge of the insert.Each projection is substantially surrounded by the body to retain theinsert in place. In particular, the portion of each projection nearestthe chisel edge is entirely covered with the die cast material of thebody to form a secure interlocking relationship between the insert andthe body.

In accordance with another aspect of the invention, a method isdisclosed for making a masonry drill in which an insert is formed from ahard material. The insert is formed with parallel planar portions oneach side and a chisel edge extending across the top of the insertbetween the sides with leading cutting edges on either side of thechisel edge and a bottom edge on the insert opposite the cutting edges.The insert is also formed with means for interlocking the insert with adrill body. The interlocking means comprises a pair of projections, oneprojection on each side extending from the plane of the side portion.Each of the projections extends the greatest distance from the plane ofthe side portion near the bottom edge of the insert. The insert isplaced in a mold for casting a drill having an axially elongated bodywith spiral grooves cast in the exterior surface of the bodysubstantially along its length. The mold is filled with molten metal toform a cast drill in the mold. The molten metal substantially surroundseach of the projections in the insert and covers the portion of eachprojection nearest the chisel edge to form a secure interlockingrelationship between the insert and the body. The cast drill is thenallowed to cool with the molten metal contracting around the insert tosecurely hold the insert in place in the drill.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the drill of the present invention.

FIG. 2 is a side elevational view of the drill taken along lines 2--2 ofFIG. 1.

FIG. 3 is a top plan view of the drill of FIG. 1.

FIG. 4 is a perspective view of a preferred form of insert used in thepresent invention.

FIG. 5 is a side elevational view of the insert of FIG. 4.

FIG. 6 is a side elevational view of the insert taken along lines 6--6of FIG. 5.

FIG. 7 is a top plan view of the insert of FIG. 5.

FIG. 8 is a bottom plan view of the insert of FIG. 5.

FIG. 9 is a top plan view of a mold used to cast the drill in accordancewith the present invention.

FIG. 10 is a side elevational view of the mold of FIG. 9.

FIG. 11 is a side elevational view of an alternative form of insert foruse in the present invention.

FIG. 12 is a bottom plan view of the insert of FIG. 11.

FIG. 13 is a perspective view of another alternative form of insert foruse in the present invention.

FIG. 14 is perspective view of still another alternative form of insert.

FIG. 15 is a perspective view of yet another alternative form of insert.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings, and initially to FIGS. 1-3,there is shown the masonry drill 20 of the present invention. The drill20 comprises an axially elongated, generally cylindrical body 21 havingat its leading or front end a tin 22 which drills into the masonry orother material. The body 21 may be of any suitable length and preferablysubstantially in excess of the deepest hole to be drilled. The body 21also has a diameter slightly smaller than that of the hole to bedrilled. At the rear end portion there is formed a cylindrical elongatedshank 23 which is adapted to be releasably clamped in the chuckingdevice of a suitable driving unit, such as a motor driven drill. Theshank 23 may be generally cylindrical with a smooth outer surface.

The body is formed with threads defining a pair of spiral or helicaldischarge channels or flutes or grooves 25. Although a single groove maybe used, a pair of grooves 25 is preferred. The spiral grooves 25 areformed in the drill body 21 along its entire length from the tip 22 tothe shank 23. In accordance with known principles of drill design, thegrooves 25 provide a means for the discharge of drilling debris duringthe use of the drill. The spiral grooves 25 are of sufficient width anddepth to be capable of conveying chips, particles and dust dislodged bythe cutting means at the drill tip 22 and operate in known manner toadvance the chips, particles and dust toward the shank 23 as the drillis rotated.

A hard insert 27 is embedded in the body 21 at the tip 22. The insert 27is arranged to extend diametrically across the end of the drill andprovides a hard cutting means for forming a hole in the material to bedrilled. The insert 27 is preferably slightly wider than the greatestdiameter of the cylindrical drill body 21 so that the insert cuts a holeslightly larger than that needed to accommodate the drill body. Aspreviously discussed, the body of the drill 21 is preferably formed witha pair of grooves 25, one of which ends on each side of the insert 27 toprovide an escape path for drilling chips, particles, dust, and otherdebris loosened by the insert 27 during the drilling operation. As shownin FIGS. 1 and 2, the leading end of each of the grooves 25 terminatesadjacent the side of the insert 27 to enable the cuttings from thematerial being drilled to freely flow through the groove and exit at therear end portion of the body. Preferably, a short, longitudinallyextending channel 28 is formed on each side of the drill body 21 at thetip 22 to provide a path for cuttings from the insert 27 to enter thegroove 25. The insert 27 is firmly embedded in the end of the body 21with leading end portions of the body extending on each side of theinsert 27, as explained in detail more fully hereinafter.

The preferred form of insert 27 is shown in more detail in FIGS. 4-8.The insert 27 preferably comprises a hard flat element having a pair ofsides which have generally flat parallel portions 29. The two flat sideportions 29 extend between two end edges formed by narrow end faces 30,as shown in the drawings. A point 32 projects upwardly from the topportion of the sides as shown in the drawings, and a chisel edge 33 isformed between these points, extending diagonally between the sides. Thechisel edge 33 forms the forward or leading end of the drill. A narrowbottom edge face 34 extends along the insert opposite the chisel edge 33between the end faces 30. A pair of cutting edges 36, each formed by thejunction of a clearance face 37 and the plane of the side portion 29,extend outwardly on each side of the chisel edge 33. The clearance faces37 are inclined in opposite directions so that the leading edge 36 ofeach of the clearance faces 37 provides a sharp cutting blade to be usedin the drilling operation as the drill is rotated.

To help secure the insert 27 in the body 21, the insert is provided withinterlocking means. In the preferred form of the tip, the interlockingmeans comprises a pair of projections 40 which extend from the plane ofeach of the flat side portions 29. When the insert 27 is embedded in thebody 21, the projections 40 are surrounded by the body material. Inparticular, the upper portions of each projection, i.e., the portions ofeach projection closest to the chisel edge 33 and to the cutting edges36, are covered by the drill body 21, making it possible to remove theinsert 27 by pulling the insert axially out of the drill body. Inaddition, the projections 40 are surrounded in all other directions bythe drill body 21 so that the insert 27 is firmly secured in the drillbody 21.

The projections 40 shown in FIGS. 4-8 are generally symmetrical on eachside, extending outwardly the maximum distance from the plane of theside portions 29 at a point 41 at the center of the edge contacting thebottom face 34, with the projection tapering toward the plane of theflat side portions 29 as it extends upwardly toward the chisel edge 33and outwardly toward the end faces 30.

The insert 27 is formed of a hard material which is resistant to wearand abrasion resulting from its use in drilling into masonry or othersimilar material. The preferred material for use in forming the insert27 is tungsten carbide, although other sintered carbides may be used,such as titanium carbide or tantalum carbide, and other hard materialsare possible. Tungsten carbide is a particularly suitable material andis preferred because of its relatively hard abrasion-resistant andrugged properties, while being less expensive than other alternativematerials which may be used and are capable of withstanding wear andabrasion. Tungsten carbide is also especially adaptable and practicalfor mass production such as the drill of the present invention.

In the making of the drill in accordance with the method of the presentinvention, the insert 27 is formed by conventional methods of powderedmetallurgy, such as by pressing and sintering. While the insert may bemade in various ways, the general method is to mold it from powderedmetal sintered or bonded together with a bonding agent in molds sizedand contoured to produce the finished insert, whereby a finish grindingoperation is not required to complete its manufacture. The inserts areformed with the preformed angled end faces 30 and clearance faces 37, sothat any finish grinding is not necessary and steps in the formation ofthe tip subsequent to the pressing operation are eliminated.

Each projection 40 (FIGS. 4-8) is generally symmetrical, and includescontoured surfaces as are formed by the tapering of the projection fromthe outwardmost projecting point 41 at the bottom center of the insertinto the plane of the flat side portion 29 of the insert, since powderdoes not readily compact into lateral protrusions during the formationof the tip according to known axial techniques of powder metallurgycompaction. It is not practical to assure the flow of powder into theprotrusions and corners, and a relatively large percentage of piecesformed in this manner would be defective as a result. By forming agenerally symmetrical projection 40 with contoured surfaces, problems ofpoor compaction and difficulty in removing pieces from the mold will beavoided, and it is possible to form the insert in a single pressingoperation, avoiding subsequent operations such as machining or grindingwhich would significantly add to the cost of fabrication of the inserts.Therefore, the insert 27 as shown in FIGS. 4-8 is particularly adaptedfor high production, low cost formation which may be used in theproduction of the die-cast masonry drill of the present invention.

During the pressing operation, the insert 27 may be formed in a contourpressing mold, and it may thereafter be easily removed with the bottomedge first, since the bottom edge contains the thickest portion of theinsert. For this reason, the placement of the point at which theprojection extends outwardly the greatest distance from the plane of theflat side portions of the insert should be adjacent to the bottom edgeof the insert so that the insert may be easily formed and removed fromthe pressing mold. To also assist in removal of the insert, theprojection is provided with generally smooth contours, avoidingrelatively sharp protrusions or steeply slanting surfaces which may tendto stick in the mold during the ejection of the finished inserts.

After forming the insert 27, it is placed in a die casting mold for theformation of the drill body. FIGS. 9 and 10 show a die casting mold 130which may be used to form the drill body using conventional die castingtechniques. The mold 130 comprises an upper half 131 and a lower half132 which are adapted to be mounted on the platens of a conventionalvertical die casting machine. A number of cartridges 133-139 may bemounted in the respective mold halves 131 and 132 to form the dies inwhich the drills are cast. As shown in FIG. 9, the combination ofcartridges 133, 134, and 135 may be used to cast a larger sized drill,while the combination of cartridges 136, 137, and 138 may be used tocast a smaller sized drill. Molten metal is supplied to the dies from agate beneath the lower mold half 132 through a passage 140 in the lowermold half and a system of runners 141. Other cartridges, such as thecartridge 139, provide an extension to the runners 141. The cartridges133-139 are held in place in the mold halves 131 and 132 by attachmentof pins 142.

With the mold halves 131 and 132 open, the inserts 27 are placed in theappropriate cartridges, such as the cartridges 135 and 138, which form aportion of the dies within which the drill is to be cast. The moldhalves 131 and 132 are then closed, by closing the platens upon whichthey are mounted. Molten metal, preferably a zinc die-casting alloy, isintroduced into the mold through the passage 140 and the runners 141. Asthe molten metal enters the mold, it fills the dies and substantiallysurrounds both of the projections 40 on the inserts. Due to the presenceof the channel 28 on the leading end of the drill, a portion of theprojection 40 adjacent to the channel may not be covered with moltenmetal or may be covered with only a thin layer of metal. After fillingthe die, the drill body is allowed to cool, and the insert is furthersecured in place by the thermal contraction during the cooling of thedie casting alloy. When the drill has cooled sufficiently, the moldhalves 131 and 132 are opened, and the finished drill is removed. Theinsert is thus cast in place on the leading end of the drill. Using themethod of the present invention, drills can be produced at high speedand very low cost.

The interlocking relationship between the projection 40 and the castbody 21 of the drill results in part from the interrelationship betweenthe material of the insert and the material of the body during theformation process of the drill. After the insert 27 has been placed inthe mold and the molten metal has been poured into the mold tosubstantially cover both sides of the insert, the drill is then allowedto cool. During the cooling operation, the die casting material of thebody of the drill contracts more than the material of the insert. Thisoccurs because the rate of thermal expansion of the die casting alloy isgreater than the thermal expansion of the typical carbide material usedin the insert. For example, the typical thermal expansion of zinc diecasting alloy used in the drill body is about 15.2 microinches per inchper degree Fahrenheit (27.4 microns/meter/°C.), while the thermalexpansion of tungsten carbide used in making the insert is onlyapproximately 3.1 microinches per inch per degree Fahrenheit (5.5microns/meter/°C.). Therefore, as the drill is allowed to cool, the bodyof the drill will contract significantly with respect to the insert.This contraction will occur on all sides of the insert. Thus, the bodywill contract around the insert and this contraction will providepressure on the insert which will serve to securely hold the insert inplace in the body of the drill. This effect may sufficiently hold theinsert in place in the drill body during operation of the drill, but themechanical interlock of the projections is also provided as anadditional means of assuring that the insert remains in place.

In accordance with one aspect of this invention, the drill body 21 isformed by casting rather than the conventional machining or grindingwhich has been used in the past to form masonry drills. Preferably, thebody 21 is formed in a die casting operation, with the material used information of the body being a known die casting alloy. The preferredmaterial for the body is a zinc alloy, although other alloys arepossible, such as aluminum die casting alloys. However, aluminum drillswould be very lightweight and might be commercially objectionable tomany users due to their apparent lack of "heaviness" and the associatedimpression of less than high quality. Zinc alloys, on the other hand,are similar in density to steel, and therefore are more commerciallyacceptable to most users, since they appear heavy. In addition, zinc maybe die-cast, has adequate strength, has a low melting point, and doesnot require a surface treatment after casting.

The use of a projection 40 on each side of the insert as an interlockingmeans is highly preferable to other types of interlocking means, such asholes or cutouts. The use of a hole or cutout could reduce the strengthof the insert, and could result in the insert fracturing during use.Also, the formation of such a hole may require an additionalmanufacturing process during the formation of the insert. Projectionscan be formed in the insert during the pressing operation of thepowdered metal, whereas, a hole or cutout may not easily be formed inthis manner and may possibly require subsequent operation after thepressing, such as machining or grinding. Furthermore, the design of someinterlocking means such as certain holes or cutouts may result in thematerial of the drill body contracting away from the surface of theinsert during cooling after the drill is cast. This contraction of thedrill body material away from the insert would result in gaps whichmight weaken the drill.

Other alternative forms of inserts are possible. One such alternative isshown in the insert 47 of FIGS. 11 and 12. The insert 47 is generallysimilar to the insert 27, with generally flat side portions 49 extendingbetween end faces 50 with a chisel edge 53 extending across the leadingend of the insert and a bottom edge face 54 opposite the chisel edge 53.A pair of cutting edges 56 formed by inclined clearance faces 57 extendfrom each side of the chisel edge 53 between the chisel edge and the endfaces 50. The insert 47 differs from the insert 27 in the form ofprojections 60 which extend from the flat side portions 49 on each sideof the insert. The projections 60 are asymmetrical with each projectionprimarily extending outwardly on the portion of the side adjacent towhich the clearance face 57 is inclined. In this manner, the projection60 does not extend to the channel 28 (FIG. 1) connecting with the groove25 at the leading portion of the body 21. The insert 47 has theadvantage that the projection is more completely covered with metalduring the casting operation, since the projection 60 is spaced awayfrom the channel 28. Thus, the projection 60 is more completely coveredby the cast material at the drill body 21 and the insert 47 is moresecurely embedded in the drill and a more secure interlockingrelationship is established. However, the insert 47 may not be as easilymanufactured in a single pressing operation, due to its asymmetry anddue to the relative steepness of the edges of the projection 60 whichmay make the insert 47 difficult to remove from the pressing mold. Thus,it may not be feasible to form the insert 47 in the pressing mold withthe projection 60 in a single operation, and it may require subsequentmachining operations, which could result in a higher production costthan the insert 27 shown in FIGS. 4-8.

Another alternative insert design is the insert 67 shown in FIG. 13. Theinsert 67 has a pair of generally flat side portions 69 extendingbetween end faces 70 and a top chisel edge 73 with a bottom edge face 74opposite the chisel edge. Projections 80 each extend outwardly from eachflat side portion 69 only directly adjacent to the edge of the bottomface 74. The insert 67 of FIG. 13 has the advantage that each projection80 does not extend upwardly toward the chisel edge 73 for a significantportion of the side of the insert. However, the different thicknesseswhich define each projection 80, in comparison to the distance betweenthe chisel edge 73 and the bottom face 74, make the insert 67 moredifficult to be formed in a single pressing operation, due to theproblems of the flow of the powdered metal and differential pressureneeded to form the projections. Therefore, it may not be feasible toform the insert 67 in a single operation, and subsequent machining orgrinding operations subsequent to the pressing of the insert in a moldmay be required. Hence, the insert 67 may be more expensive tomanufacture than the insert 27.

Another alternative insert design is shown in FIG. 14. This insert 87 isgenerally similar to the insert 67 shown in FIG. 13 with flat sideportions 89, end faces 90, a chisel edge 93, and a bottom edge face 94,but the insert 87 has a pair of projections 100, each of which may bethicker than the projection 80 and each of which extends to one of theend faces 90 but terminates short of the other end face so that theprojection does not extend to the channel 28 and may be completelycovered with the material of the drill body to provide a more secureinterlocking relationship. As with the insert 47 of FIG. 11, the insert87 of FIG. 14 has the advantage of projections spaced away from thechannels 28 so that the projections may be completely covered withmolten metal during the casting of the drill body, and as with theinsert 67 of FIG. 13, the insert 87 has projections which do not extendupwardly toward the chisel edge for a significant portion of each sideof the insert. However, the insert 87 of FIG. 14 may not be formed by asingle pressing operation and may require subsequent machining orgrinding, as with the inserts 47 and 67 of FIGS. 11 and 13.

Another alternative insert design is shown in FIG. 15, in which aninsert 107 has flat side portions 109, end faces 110, a chisel edge 113,and a bottom edge face 114. The insert 107 has a pair of projections 120each of which extends from the bottom edge face 114 toward the chiseledge 113, with each projection slanting inwardly toward the center ofthe flat side portion 109 as it extends upwardly. The projections 120 donot extend to the channel 28 and extend a substantial distance along thesides of the insert 107 to enhance the interlocking capabilities.However, the insert 107 may be difficult to produce economically, due tothe shape of the projection 120.

Other modifications and variations are possible. For example, a steelcore or other reinforcing core may be inserted in the drill body 21.Such a core would be placed in the die casting mold prior to theintroduction of the molten metal used to form the drill body and wouldserve to reinforce the body of the drill and prevent breakage of thedrill under especially extreme conditions. The insert may also be brazedon the leading end of the reinforcing core to further secure the insertin the drill body.

While the invention has been shown and described with respect tospecific embodiments thereof, it will be apparent to those skilled inthe art that other variations and modifications of the specific formherein shown and described may be used without departing from the spiritand scope of the invention. Accordingly, the patent is not to be limitedin scope and effect to the specific embodiments herein shown anddescribed, nor in any other way which is inconsistent with the extent towhich the progress in the art has been advanced by this invention.

What is claimed is:
 1. A drill adapted for use in drilling masonry orother hard, brittle material, which comprises:an axially elongated,generally cylindrical body having a leading front end portion and a rearend portion, said rear end portion adapted to be held by a tool holder,said body being formed of a die cast material and having at least onespiral groove cast in its exterior surface substantially along itslength; and a hard insert embedded in the leading end of said body, saidinsert being generally flat and extending generally diametrically acrosssaid leading end of said body, the sides of said insert having parallelplanar side portions and a chisel edge across the top of said insertwith leading cutting edges on either side of said chisel edge and abottom edge on said insert opposite said cutting edges, said inserthaving means for interlocking with said body, said interlocking meanscomprising a pair of projections each extending from the plane of one ofsaid flat side portions, each of said projections extending the greatestdistance from the plane of said side portion near said bottom edge ofsaid insert, said projections being in a contiguous relationship withsaid body and substantially surrounded by said body to retain saidinsert within said body without the addition of other securing material,the portion of each of said projections nearest said chisel edge beingentirely covered with said die cast material of said body to form asecure interlocking relationship between said insert and said body.
 2. Adrill as recited in claim 1, wherein each of said projections isgenerally symmetrical about an axis extending normally from said bottiomedge to said chisel edge of said insert.
 3. A drill as recited in claim1, wherein each of said projections tapers inwardly toward the plane ofsaid flat side portions of said insert as said projection extends fromsaid bottom edge toward said cutting edges.
 4. A drill as recited inclaim 1, wherein each of said projections extends the greatest distancefrom the plane of said flat side portions at said bottom edge near thecenter of said insert, and each of said projections tapers inwardlytoward the plane of said flat side portion as said projection extendsoutwardly toward the ends of said insert.
 5. A drill as recited in claim1, wherein said projection is formed with generally smooth contours. 6.A drill as recited in claim 1, wherein the coefficient of thermalexpansion of said die cast material of said body is greater than that ofsaid insert.
 7. A drill as recited in claim 1, wherein said die castmaterial of said body is a zinc alloy.
 8. A drill as recited in claim 1,wherein said hard insert is formed of tungsten carbide.